Figure 3.

(a) The two-leveled chamber used to deflate the vesicles. The top chamber was filled with glucose solution with a higher osmolarity than the solution encapsulated inside the vesicle. To image the vesicles, the entire chamber was closed and put on the microscope stage. (b) Deflation of the cortex-free vesicles shows the well-documented shape transformations due to the Helfrich-energy minimization. (c) For the passive cytoskeletal vesicles, the change in external osmotic pressure does not immediately cause any shape remodeling (from point I to II) but causes a continuous shape remodeling for active vesicles (from point I to III). (d) Phase-contrast images of passive (red panel) and active (blue panel) cytoskeletal vesicles at time points indicated in (c). The active vesicle is able to remodel the cytoskeleton and deforms actively while the pressure changes from I to II, whereas the passive vesicles resist the increasing osmotic pressure at first. At point III, both vesicles, the passive and the active ones, have reached a highly deformed shape with similar reduced volumes. Similar deformed shapes are observed for both the active and the passive vesicles although via different trajectories. For the passive vesicles, deformations appear abrupt, whereas for active vesicles, a continuous deformation is observed. The curves in (c) are the average values taken over five vesicles for the passive case and eight vesicles for the active case. The error bars are the SDs on the measure of the mean contracted radius <r>. We computed the Kruskal-Wallis test at the point II and second step (right before the passive vesicles crumple). The p-value comparing the data sets of active and passive vesicles are p = 0.032 and p = 0.044, respectively. Scale bars, 20 μm. To see this figure in color, go online.